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Author Topic: Before Somebody Gets Hurt: What is Safe Limit on Flywheel Speed?  (Read 3475 times)
quinnf
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« on: January 06, 2006, 09:12:23 pm »

Just noticed an engine selling on e-bay #7578704005.¬  The ad indicates it is a 16/1 with 27" flywheels turning 1000 rpm.¬  Picture shows 6-spoke flywheels just like on a 650 rpm engine.¬  I recall something on one of the old engine sites about maximum rim speed for good quality tight grained cast iron flywheels not to exceed 5000 ft/min.¬  Most Indian iron is neither good quality, nor close-grained.¬ 

This is about 33% faster than that limit, and centripetal force increases as the square of the rotation speed.¬  Garden-variety 6/1 'roid turns about 4100 ft/min.¬  Higher speed 'roids lose the 6-spoke flywheels in favor of a solid and smaller diameter wheel.¬  This one doesn't.¬ 

Here's another reference that says the same thing:

http://www.rustyiron.com/engines/flywheel/index.html

Quinn



« Last Edit: January 06, 2006, 09:36:57 pm by quinnf » Logged
SHIPCHIEF
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« Reply #1 on: January 06, 2006, 11:45:17 pm »

I was checking this out in Machinery's Handbook 25th edition at work last week. Sorry I don't have it at home (I'm on days off) but I recall something about 20 inch flywheels in cast iron being limited to 1050 RPM or such, with a design safety factor of 10 being required for flywheels.
Someone (Like Jack) who has a Machinery's on hand and has read it more than I have should weigh in on this. This is an area that is clearly established by laws and engineering practice, we just need to find and obey it.
Oh, and keep those gib keys tight! I just heard another story about a flywheel walking out. It was caught in time, so no harm, but I keep mine held in by additional collars. I have a V belt pully on one end and my starter ring gear on the other, they are butted against the gib keys. Cheesy
Scott E
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quinnf
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« Reply #2 on: January 07, 2006, 02:34:53 am »

Scott,

If you can find that reference it would be nice.  I'd like to know what the standards are before I e-mail the guy.  I'm concerned that someone is going to get hurt. 

The scary thing about flywheels is the amount of energy they store.  I had some spare time today at work and calculated the centripetal force on the rim of a flywheel.  A 6/1 at 650 rpm is pulling 141 Gs at the rim.  So in a catastrophic failure a 10 lb. chunk would be traveling 46 mph, and would impact with a force of 1400 lbs.  The 16/1 that the e-bayer is selling is pulling with a force of 384 Gs, and from the pictures it doesn't look like that flywheel was beefed up at all. 

When you double the rotational speed, the force increases 4 times.  And when you increase the diameter of the flywheel, that increases the centripetal force by the square of the radius, so you combine the additional speed and larger diameter and that thing is a timebomb.  One flaw in the casting is all it would take.

Quinn
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kpgv
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« Reply #3 on: January 07, 2006, 07:37:50 am »

Quinnf,

I saw the same listing you referenced, and I kind of figured it was a misprint, but....
The last thing we need is someone importing "virtual" bombs Angry
I have a "Machinerys Handbook" (22 ed.)  here to reference from regarding flywheels:
P)228
  Centrifugal Stresses in Flywheel Rims_

"The centrifugal tension or hoop tension stress which tends to rupture a flywheel rim of given area, depends solely upon the rim velocity, and is independent of the rim radius. The bursting velocity of a flywheel, based on hoop stress alone (not considering bending stresses), is related to the tensile stress in the flywheel rim by the following formula which is based on the centrifugal force formula from mechanics.

            V = square root of (10xs) or, s = V squared divided by 10

where V = velocity of outside circumference of rim in feet per second, and s = the tensile strength of the rim material in pounds per square inch.

For cast iron having a tensile strength of 19,000 pounds per square inch the bursting speed would be:

V = square root of (10 x 19,000) = 436 feet per second"

The trouble with this formula is that it is based on (I think) a solid center (not spoked) wheel,
because on p230 & p231 there are charts that clearly state:

"Safe rim speed for "balance wheels"- heavy rims- 110 ft/sec and 6600 ft/min."

Also, on p230, it is stated:

"To find the safe speed in revolutions per minute, divide the safe rim speed in ft/min. by 3.14(pi) times the outside diameter of the flywheel rim in feet."

For the 16/1 @ 1000rpm w/ 27" flywheel engine in question:

6600ft/min divided by (3.14 x 2.25') = 933.7 rpm..... Shocked Shocked Shocked..... for an engine rated at 1000 rpm....Buyer Beware Shocked Shocked Shocked

Also, as Quinnf pointed out, there in no way to know if the iron used in these is anywhere near the quality used in these formulas.
This is a damn good case why engineers use "safety factors" like 10x or MORE!!!

Get a copy of this book if you can!!!  DON'T worry about the "edition" number!!! My Dad has one from~1950... This kind of mechanical and design information hasn't changed. New ones just have more "metric" info.

Curious what the deal is w/ these engines Huh Huh Huh

Kevin

 


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hotater
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« Reply #4 on: January 07, 2006, 05:06:51 pm »

I've been in a tizzy---

I work as an expert witness involving mechanical devices of specific nature.  In this work I deal with mechanical engineers regularly

 AFTER somebody wipes out a garage, house and his or somebody else's kids is way too late.¬† ¬†

This morning I contacted the seller through the ebay 'ask a question' feature with this:


SERIOUS SAFETY CONCERNS!!!  Sir, I've been working on these engines for more than a year and work every day with mechanical engineers.. We feel your advertized engine is dangerous by design and by material and poses a SERIOUS risk of death or serious injury by the user and bystanders. IT's a grenade!!
 Under Federal tort law, you're obligated to WARN the buyer of any defect, in writing, before sale.
  Personally....there's NO way I'd sell that engine...it's dangerous by design and any engineering book or cast iron pulley resource will substantiate that in five minutes.  You're on the wrong end of slam dunk lawsuit.

Jack Belk-- hotater, at listerengine forum.


So far I've received no reply.

The next step is contact ebay and have it pulled.  THIS is BS of the first water and can't be allowed.

I'd do the same thing if I saw someone advertizing a cast iron rifle barrel.  The same physics apply.
 The obvious next step is somebody deciding since he's already got the same engine, all he has to do to get more HP is turn up the wick.  Misinformation hangs around a LONG time.
 Like Paul Harvey says,  "You can't unring a bell"
« Last Edit: January 07, 2006, 05:11:28 pm by hotater » Logged

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rpg52
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« Reply #5 on: January 07, 2006, 05:20:38 pm »

I ran across an account from Australia about someone with a Lister in a pump house that lost a gib key and a flywheel.  The flywheel went through the shed wall and was found 2 Km away!  The owner was able to repair it, but it's a good illustration of the danger involved.
Ray
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Stan
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« Reply #6 on: January 07, 2006, 11:05:24 pm »

http://www.agroengine.com/diesel1.htm

The above url shows 1 cyl Listeroids with identical bore and stroke running from 6hp right up to 16hp.  I tried to contact them some months ago to see what was different about the engines with differeing hp other than rpm.  They couldn't give me a definitive answer.  I wonder what the rpm and "rim speed" of their flywheels are?
Stan
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Isn't it strange that people are happy to adopt epithets they would fight to the death to throw off had they been imposed?
kpgv
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« Reply #7 on: January 10, 2006, 11:55:39 pm »

I've seen that site too. Some of those engines are (must be) twins. Roll Eyes
Look at the listed bore & stroke & RPM info...
Alas, No flywheel diameter info. Tongue

Kevin
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kpgv
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« Reply #8 on: January 11, 2006, 10:00:48 pm »

I've been thinking about this 16/1 @1000rpm with the 27" flywheels.
I think we agree the rim speed is likely too fast and unsafe.
I'm wondering if it could still be a good rig if one just replaced the flywheels with the ~20 inchers that are on the other 1000rpm engines??? (assuming it could be re-balanced???), or just slow it down to ~500rpm and have an ~8/1???

Kevin 
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Stan
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« Reply #9 on: January 11, 2006, 11:07:47 pm »

The Lister JP, JS & JK engins started with the JP at 9 hp 1 cyl 1000rpm.  Don'k now what size the flywheel was though.  Will try and look it up.
Stan
btw  they came in 18/2,  21/2,  30/3, 40/4 and 61/6 configurations also. Grin
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trigzy
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« Reply #10 on: January 12, 2006, 04:50:04 am »

There also seems to be some confusion in his listing.  On spot says 27" flywheel, another says 2 foot flywheel.  So maybe you needn't be getting this excited?  The listing makes it pretty obvious to seasoned eBayers that he doesn't know what he's doing.  The flywheel might not even be soild iron - could be steel or something.  Way too many variables here.


Steve
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quinnf
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« Reply #11 on: January 13, 2006, 07:35:03 am »

Steve,

I understand where you are coming from, but even a 24" 6-spoke flywheel spinning that fast is dangerous, and if you look at the nameplate on the engine with that 6-spoke flywheel, you can't quite make out what the horsepower is, but it doesn't look like it says 6.5.  Looks like the first digit is a "1."

Steel flywheel?  From India?  That would be a first (great idea, though).  Well, it appears to be a seller that isn't very sophisticated and is buying from a vendor that does some really weird things to save a rupee or three (e.g. placing two 6/1 heads on a 12/2 crankcase and calling that a 12/2), so that makes me nervous.  For us to just sit here and do nothing would be wrong.  Should the worst happen, it would also be easy and in character for some politician to finesse a ban on the operation of exposed flywheel engines.  The import of these wonderful engines to could also be restricted or simply halted.  The EPA is already lumbering down that path.

If someone were to get hurt/killed by an exploding flywheel, that would be tragic.  The centripetal force at the rim is appx. 320 Gs.  The rim is rotating at over 70 mph.  Kinetic energy increses as the square of velocity.  Imagine what a 10 or 20 lb. chunk of broken cast iron travelling at 70 mph would do to anyone standing nearby.

Jack (hotater), probably the best qualified among the denizens of this board to do so, has politely and non-confrontationally warned the seller about the issues involved. 
The seller has not bothered to reply.  What does that tell you?

Quinn
« Last Edit: January 13, 2006, 07:41:38 am by quinnf » Logged
trigzy
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« Reply #12 on: January 13, 2006, 12:11:56 pm »

Quinn,
        I would like to do something as much as you do.  However, what to do is not very obvious.  As far as getting eBay to pull the listing, by all means, go ahead and try, but eBay isn't usually worried about safety.  I emailed them multiple times about people selling non-CSA (or other approval) generators here in Ontario (Illegal to advertise, sell or buy) but they refused to do anything about it.  Why?  Because I'm not an enforcement offical.  But if I was, well, eBay would those listings down so fast it would make your head spin.  eBay wants to get the most sales they can, and whether or not a product is safe or not doesn't stop eBay from collecting thier closing fees.

Steve
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SHIPCHIEF
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« Reply #13 on: January 14, 2006, 05:02:43 am »

I rechecked Machinery's Handbook on this issue. If the flywheels on the engine we are talking about are 24" as stated in the latter part of the ad, the design limit is 1050 RPM.
"Cast iron flywheels are commonly designed with a factor of safety of 10 to 13. A factor of safety of 10 applied to the tensile strength of a flywheel material is equivalent to a factor of safety of  the square root of 10 or 3.16 on the speed of the flywheel due to the fact that the stress on the rim of a flywheel increases as the square of the speed"...
The burst speed (mentioned on the next page) is about 3.59 times the design speed for cast iron wheels having solid rims. The 6 spoke flywheel has a conversion factor of 1.0 so it must be the baseline for calculation. I couldn't really speak to the rim thickness calcs and other unknowns. I did not go into the calcs for engine flywheels which refers to tortional vibrations due to variations in energy during each stroke. Huh These variables would serve to reduce that safe rated speed of the flywheel further.
If the wheels are 27's that's outside the 935 RPM limit, if they are 24's it's 1050 RPM, allowing a 5% overspeed, not much of a tolerance for the limit. The 20" flywheels on my engine would be limited to 1260 RPM, a more comfortable margin.
Considering the forms of acceleration that can effect the flywheel while at speed, I am reluctant to endorse any kind of resilliant engine mount that allows the engine to move on the bed. I am continually brought back to the original instruction and Hotater's advice to lock that engine down on a yard of concrete.
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Ashwamegh 25/2 & ST12
Lister SR2 10Kw 'Long Edurance' genset on a 10 gallon sump/skid,
Onan 6.5NH in an old Jeager Compressor trailer and a few CCK's
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